1. Field of the Invention
The present invention relates to an actuator, a method of controlling the actuator, and a camera module including the actuator, and more particularly, to an actuator, a method of controlling the actuator, and a camera module including the actuator that are adapted for moving a lens assembly along an optical axis using a voice-coil-actuator-type driving part configured to apply an electric current to a coil within the magnetic field of a magnet, and adapted for using a frictional force to prevent the lens assembly from returning to its initial position when the applying of the electric current is stopped.
2. Description of the Related Art
In general, as methods of manufacturing a mobile communication terminal including a digital camera or a camera module are developed, camera modules are miniaturized and lightened.
Recently, as the number of pixels in camera module packages for a mobile communication terminal is increased and functions of the camera module packages are improved, the camera module packages are dramatically developed so as to obtain the performance of high quality digital cameras. Particularly, various studies are carried out for realizing an auto focusing technology in the size of the camera module package for a mobile communication terminal.
Actuators, configured to realize the auto focusing technology, are classified into a voice coil actuator (VCA) using a Lorentz force and a piezo actuator using a piezoelectric effect.
The voice coil actuator includes a support part and a driving magnet part. The support part, supporting a lens assembly, includes a spring member that returns the lens assembly to its initial position when an electric current is not applied. The driving magnet part generates the Lorentz force by applying the electric current to a coil disposed within a magnetic field generated by a magnet, so as to move the lens assembly along an optical axis.
The voice coil actuator moves the lens assembly along the optical axis using the Lorentz force generated by applying the electric current to the coil disposed within the magnetic field generated by the magnet, and the spring member returns the lens assembly to its initial position when the applying of the electric current is stopped.
The piezo actuator moves a lens assembly by repeatedly applying pulse signals to a piezoelectric element, and returns the lens assembly to its initial position using a ball bearing or a sliding bearing replacing a support member such as a spring.
The instability of a spring in the voice coil actuator causes malfunctions including tilting and decentering according to part variations or assembly variations, and an electric power must be continuously supplied to keep the lens assembly at a position displaced in a predetermined extent from force equilibrium.
Also, when the lens assembly returns to its initial position, great stress is exerted on the spring, thereby decreasing reliability.
The lens assembly of the piezo actuator moves more stably than that of the voice coil actuator, but material costs of the piezo actuator is higher than those of the coil or the magnet, and requires an additional position sensor because of the uncertainty of friction.
Thus, an actuator for a camera module is required for addressing the limitations of the voice coil actuator and the piezo actuator and taking the advantages thereof.